The few chimpanzees still used for biomedical research in the United States can live in much tighter quarters than some experts prefer. The National Institutes of Health (NIH) has decided that about 23 square meters (250 square feet) per individual is adequate. That is just one-fourth the area that an advisory committee had recommended.

The space plan affects a dwindling number of research chimpanzees. In December 2011, an Institute of Medicine (IOM) report found that most research on chimpanzees is unnecessary and that NIH should limit the animals’ use. After asking an advisory committee to help it carry out IOM’s advice, NIH announced last June[2] that it would retire to sanctuaries all but 50 of its 360 research chimpanzees and impose new requirements on any remaining NIH-funded behavioral and biomedical studies.

The one sticking point, however, was the advisers’ recommendation that an individual chimpanzee have at least 93 square meters (1000 square feet) of primary living space. NIH said there was little evidence to support that amount of space, which could be costly, especially because the chimpanzees were supposed to live in groups of at least seven animals. So the agency decided to get input from experts on animal care and commission a literature review.

NIH has now concluded that the smaller area is sufficient. The one research team that has studied chimpanzee enclosure size in zoos concluded that once the animals have at least 12.2 square meters per individual, the benefits of more space taper off, NIH says in a notice today[3]. More important than space is that animals have room to climb and “complexity,” such as places to hide from other animals, it says. (The new minimum is 10 times larger than the current required enclosure size.)

The Humane Society of the United States, which has pushed to end invasive chimpanzee research, is “disappointed,” comments Kathleen Conley, vice president of animal research issues at the organization. She says the experts NIH consulted with are all from research laboratories. “They can't expect people to support this recommendation with such a biased process,” she said in an e-mail.